In order to analyze characteristics of substances, a measurement method in which a measurement object is held by a void-arranged structure (a structure having a plurality of voids), the void-arranged structure holding the measurement object is irradiated with electromagnetic waves, and then a transmission spectrum thereof is analyzed to detect the characteristics of the measurement object has been conventionally used. To be more specific, a method in which a measurement object, such as a protein, that is attached to a metal mesh filter is irradiated with terahertz waves so as to analyze the transmission spectrum can be cited, for example.
As a conventional technique of the transmission spectrum analysis method using electromagnetic waves as described above, for example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2008-185552) discloses a measurement method in which electromagnetic waves are emitted to strike a void-arranged structure having a void region (specifically, a mesh-formed conductor plate), where a measurement object is held, in an oblique direction with respect to a principal surface of the void-arranged structure, and the electromagnetic waves that have passed through the void-arrange structure are measured so as to detect characteristics of the measurement object based on a phenomenon that the position of a dip waveform generated in the measured frequency characteristic moves depending on presence/absence of the measurement object.
In addition, Patent Document 2 (International Publication No. WO 2011/027642) discloses a measurement method in which a void-arranged structure having a void whose shape is not mirror-symmetric with respect to an imaginary plane orthogonal to a polarizing direction of electromagnetic waves is used, and the void-arranged structure is irradiated with the electromagnetic waves in a direction perpendicular to a principal surface of the void-arranged structure so as to measure characteristics of the measurement object using the frequency characteristic of the electromagnetic waves having been scattered. In this method, because the electromagnetic waves strike the void-arranged structure in the direction perpendicular to the principal surface of the void-arranged structure, measurement errors due to a variation in incident angle of the electromagnetic waves can be suppressed in comparison with the case where the electromagnetic waves strike the void-arranged structure in the oblique direction. Accordingly, this method has an advantage that measurement sensitivity can be improved.
However, a measurement method that exhibits a higher sensitivity and a higher reproducibility than the above-described methods has been required to be provided.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-185552
Patent Document 2: International Publication No. WO 2011/027642